Anthropology, The Field Museum, Chicago
Friday 3:45-4:00, Ballroom B
The existence of a fertile window in the human menstrual cycle, lasting just a few days bracketing mid-cycle ovulation, has long been accepted. Duration of the window has often been restricted to 3 days, allowing 48 hours for sperm survival and 24 hours at most for egg survival. This “eggtimer” model has been recognized as generally typical for Old World monkeys, apes and humans. Yet it has also been accepted that mating often extends outside the fertile window, potentially throughout the cycle in humans. But mating on the boundaries of the fertile window introduces the danger of fertilization with senescent gametes. For gestation periods inferred from intervals between single matings and births, coefficients of variation are typically about ±2% across mammals (including prosimian primates), but approximately twice that level in higher primates. Doubled variability of gestation lengths in higher primates is unlikely, so the problem seemingly resides in equating mating with conception. Possibilities for sperm storage in the uterine cervix and/or oviduct have rarely been considered for humans or other higher primates. But evidence from clinical studies and procedures such as artificial insemination indicates that sperm storage for ~10 days is a real possibility, at least for humans. Moreover, analysis of data for pregnancies following single copulations indicates an extensive window for conception in the human cycle. These findings have important implications both for studies of reproduction in non-human primates and for human reproductive biology.
This research was not supported by a grant from any funding agency.